Communication devices such as wireless devices are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a wireless communications system or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications system.
Wireless devices may further be referred to as mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as wireless device or a server.
The wireless communications system covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the area of radio coverage provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells, and may have co-located or distributed antennas. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless devices within range of the base stations. Some base stations may be multi-standard radio (MSR) base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP GSM EDGE Radio Access Network (GERAN), a wireless device has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. EDGE is an abbreviation for Enhanced Data rates for GSM Evolution. In the end of 4008 the first release, Release 8, of the 3GPP Long Term Evolution (LTE) standard was finalized and later releases have also been finalized.
In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In a wireless communications network, radio transmissions on one frequency create co-channel interference but may also cause interference or noise on another frequency, where the other frequency may be an adjacent or non-adjacent channel, in the same or other frequency band. Interference sources may be categorized as:                (1) Co-channel (interferer, a.k.a. aggressor, and victim use the same frequencies); and/or        (2) Inter-channel Interference (aggressor and victim use different frequencies), such as,                    Out-of-band emissions,            Spurious emissions,            Unwanted emissions,            Adjacent channel interference & receiver selectivity,            Spurious responses,            Intermodulation, and/or            Receiver blocking and receiver overload.                        
The term inter-channel interference reflects a series of potential interference issues that may occur throughout a communications system's service area on one channel due to radio communications activity on another channel. Inter-channel interference is a function of the performance of both transmitters and receivers.
Out-of-band emissions. Transmitter emissions that fall outside of the transmitter's intended channel bandwidth are known as out-of-band emissions (OOBE) or, equivalently, as sideband noise. This noise splatters into the adjacent channels and into other bands, generally decreasing in strength with the frequency offset from the transmitter frequency.
Spurious emissions. Emission on a frequency or frequencies which are outside the transmitter's intended channel bandwidth are known as spurious emissions, and the level of spurious emissions may be reduced without affecting the corresponding transmission of information.
Unwanted emissions. Unwanted emissions consist of spurious emissions and out-of-band emissions.
Adjacent channel interference and receiver selectivity. Desensitization, or ACS (Adjacent Channel Selectivity), is a measure of a receiver's ability to receive a wanted signal at its assigned channel frequency in the presence of an adjacent channel interfering signal at a given frequency offset from the centre frequency of the assigned channel, without the interfering signal causing a degradation of the receiver performance beyond a specified limit.
Adjacent Channel Leakage Ratio is a measure of the power which leaks into certain specific nearby Radio Frequency (RF) channels as a result of transmitting in a given channel. It provides an estimate of how much a neighbouring radio receiver will be affected by the Out Of Band (OOB) emissions from a transmitter. It is defined as the ratio of the filtered mean power in a set bandwidth within the wanted channel to the filtered mean power in an adjacent channel.
Spurious responses. It is common for transmitters to have elevated power levels at a small number of discrete frequencies other than the intended transmitter frequency. Likewise, receivers exhibit somewhat elevated sensitivity at a small number of discrete frequencies outside the intended receive frequency bandwidth.
Intermodulation. Receiver intermodulation (IM) is the result of mixing two or more over-the-air signals within a radio's receiver circuitry such that the mix products fall within the Intermediate Frequency (IF) bandwidth of the receiver and add to its thermal noise floor, thus reducing the sensitivity of the receiver. IM is not due to the transmitter's spectrum output but to non-linearity within the receiver itself.
Receiver blocking. Describes a situation when the receiver front end can be overloaded by a single high level unwanted signal, residing outside of the desired channel, or multiple high level unwanted signals.
Transmit-receive scenarios are common interference scenarios, especially in unpaired spectrum, but also with paired spectrum with multiple systems in the same area. Some example interference scenarios caused by DL radio transmissions are illustrated in FIG. 1. There are also interference scenarios cause by UL radio transmission or a combination of both DL and UL transmissions.
FIG. 1 illustrates examples of scenarios of adjacent or other-channel interference from DL (downlink) transmissions on frequency f1: (a) to a device communicating with another system (e.g., a satellite) on frequency f2; (b) to a device receiving DL transmissions from a radio node on frequency f3; (c) to a radio node receiving UL (uplink) transmissions from a device on frequency f4, where the radio node may belong to own system (e.g., with FDD or frequency division duplex where DL and UL transmissions are on different frequencies) or other system; and (d) to a device communicating with another device using frequency f5.
The amount of inter-channel interference and the caused performance degradation of a victim system may be significant. Managing the inter-channel interference may thus be important for spectrum management, network planning, network deployment, and/or network operation tasks. To provide good/improved co-existence performance of multiple systems and control an amount of allowed emitted power and unwanted emissions as well as a receiver ACS capability, the 3GPP (3rd Generation Partnership Project) standard specifies RF transmitter and receiver requirements, e.g., spectral masks, ACLR (Adjacent Channel Leakage Ratio), ACS, etc., which are defined for both user equipment and radio nodes.
Radio Requirements
The UEs (i.e., user equipment nodes or wireless devices or terminals) and base stations may be required to fulfill a specified set of RF transmitter and RF receiver requirements to provide that the wireless devices limit interference and are able to handle a certain level of interference respectively.
More specifically, out of band (OOB) and spurious emission requirements are to be met as part of RF transmitter requirements. An objective of OOB and spurious emission requirements is to reduce/limit the interference caused by the transmitters, e.g., User Equipment (UE) and/or Base Station (BS) transmitters, outside their respective operating bandwidths to the adjacent carriers or bands. In fact, wireless communication standards such as Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Evolved UTRAN (E-UTRAN), Wireless Local Area Network (WLAN) etc., clearly specify the OOB and spurious emission requirements to reduce, limit, and/or minimize unwanted emissions. These requirements may be primarily approved and set by the national and international regulatory bodies, such as, ITU-R (International Telecommunications Union—Radiocommunications Sector), FCC (Federal Communications Commission), ARIB (Association of Radio Industries And Businesses), ETSI (European Telecommunications Standards Institute), etc.
Unwanted emission requirements, which may be specified by the standardization bodies and eventually enforced by the regulators in different countries and regions for both UE and the base stations may include:                (1) Adjacent Channel Leakage Ratio (ACLR);        (2) Spectrum Emission Mask (SEM);        (3) Spurious emissions; and/or        (4) In-band unwanted emissions.        
Specific definitions and/or specified levels of these requirements may vary from one system to another. Typically, these requirements provide that emission levels outside an operating bandwidth or band in some cases remain several tens of decibels (dB) lower compared to the wanted signal in the operating bandwidth. Although OOB and spurious emission level tend to decay dramatically further away from an operating band, they may not be completely eliminated, at least in the adjacent carrier frequencies.
Significant RF receiver requirements, which are typically specified by the standards bodies and in some cases enforced by the regulators in different countries and regions for both UE and the base stations include:                (1) Receiver sensitivity;        (2) Adjacent Channel Selectively (ACS);        (3) In-channel selectivity;        (4) Spurious emissions; and/or        (5) Blocking: in-band, out-of-band, narrow-band, etc.Operating Bands in 3GPP        
The currently specified operation bands for Evolved Universal Terrestrial Radio Access (E-UTRA) are shown in Table 1 of FIG. 2. The embodiments described herein, however, are not limited to E-UTRA bands, 3GPP bands, or even licensed bands in general.
Spectrum Management and Guard Bands
A significant step in the development of interference avoidance mechanisms is the creation of a spectrum database. It may also be important to supplement this allocation and assignment data with information regarding the actual use of the airwaves. Indeed, a more complete database may include additional information such as temporal duty cycles, and active and inactive time periods. The analysis of the inventory information along with any data on the actual use of spectrum may take into account the purpose for which a spectrum band in question has been originally allocated. For example, in some bands, it may be appropriate to look at average spectrum utilization over a given period of time or over a certain geographic area. For other bands, utilization could be based on peak usage levels, especially during times of emergency.
Configuring guard bands is one of the basic inter-channel interference, mainly adjacent channel interference, avoidance techniques. The part of the spectrum constituting a guard band is either unused or is partially used by the wireless device. The latter is also known as restricted operation or guard band comprising the restricted use of radio resources. More specifically the partial or limited use may mean, for example, that the transmitter is allowed to transmit at lower power level, e.g. up to 0 dBm in guard band, whereas up to 43 dBm may be transmitted in normal (non-guard band) portions of the spectrum.
A guard band is an allocation of spectrum used to separate adjacent transmit and receive bands within a given service or to separate bands of different services for the purpose of protecting operations within the separated bands from interference. Guard bands allow sideband noise and filter responses to roll off to acceptable levels before entering other bands. A guard band may be helpful, for example, to account for practical limits of filters used to prevent strong off-channel signals or emissions from entering receivers while enabling reducing out-of-channel signals or emissions to levels sufficient to protect the receiver. The guard band spectrum is typically designated for another type of service that, due to its particular use case, is neither significantly affected by interference from the adjacent bands nor significantly interferes with the adjacent bands.
Unused band, unused spectrum, restricted band, restricted spectrum, and/or restricted resource blocks are some of the alternate terminologies used to describe guard bands. All of these terms may have substantially the same meaning, i.e., part of unused spectrum or spectrum with limited use to reduce/prevent interference between 2 wireless systems.
Formal Guard Band Allocation
Frequency coordination may be an effective method in which a guard space is used to separate systems sharing the same frequency spectrum or occupying adjacent frequency spectrum. Frequency coordination is usually thought of as a formal process by which a frequency and a coverage area are assigned to an applicant. Guard bands may then be statically decided by a regulatory body. The guard band may also be decided mutually by the individual parties operating their systems in adjacent bands or carriers. For example, operator A and operator B operating LTE (Long Term Evolution) TDD (Time Division Duplex) systems using adjacent carrier frequencies may decide to keep a guard band of 5 Mega Hertz (MHz). This can be realized, for example, using equal spectrum contribution from each operator (i.e., each operator may agree to set aside 2.5 MHz of unused spectrum). An example of a guard band is illustrated in FIG. 3 for an 800 MHz land-mobile band and an associated guard band.
The statically assigned guard bands may not be efficient from a spectrum utilization point of view. Furthermore, they may or may not be sufficient, depending on the location of transmitters and receivers and the transmit power level. Additional means of dealing with the interference may thus be used as discussed below.
Duplex antenna combining. Duplexing is a way to reduce interference when an antenna is shared by a transmitter and a receiver. The technique includes combining, for example, a base station's transmitter antenna and receiver antenna into a single antenna through a duplexer which attenuates the transmitter's signal and reduces/prevents entry of the transmitter's signal into the receiver to a practical extent.
Physical separation of BS transmitter antenna(s) and BS receiver antenna(s) (see FIG. 4a). As shown in FIG. 4a, for example, a statically allocated 2 MHz guard band may be sufficient for non-collocated BS transmitters and receivers, but not for BS transmitters and receivers located at a same antenna tower. In FIGS. 4a, 4b, 4c, the terms “mobile Tx” refers to a mobile terminal that is transmitting, “mobile Rx” refers to a mobile terminal that is receiving, “base Tx” refers to a base station that is transmitting, and “base Rx” refers to a base station that is receiving.
Interference between mobile transmitter and mobile receiver (see FIG. 4b). A guard band between UE (mobile) transmitter frequency spectrum and UE (mobile) receiver frequency spectrum may be less practical because a large guard band may be needed compared to the BS-to-BS case due to more relaxed requirements for mobiles and practical filter limitations.
Effective guard bands by geographical reuse for BS-to-mobile and mobile-to-BS scenarios. By exploiting geolocation of transmitters and receivers and by exploiting the fact that the inter-channel interference for BS-to-mobile and mobile-to-BS may typically be less significant (e.g. due to height difference or isolation), a true guard band may be omitted. For example, see FIG. 4c. 
In general, guard bands may be very effective at reducing effects of OOBE from narrowband systems because the OOBE of a narrowband transmitter may roll off significantly in a practical-sized guard band (e.g., approximately 1 MHz). Broadband signals, however, may have broader OOBE spectrums, and aggressive filtering may still be required to substantially reduce OOBE with a 1 MHz guard band, which may only be practical at base stations.
In some exceptions, a slightly higher performance degradation may be accepted as a worst case while allowing for a more dynamic guard band control. For example, to reduce/prevent OOBE from 700 MHz C Block LTE mobile transmitters from interfering with public safety mobiles in the 700 MHz public safety block, a special mode was created in the 3GPP standard that results in lower OOBE but also reduces throughput. The special mode is under the control of the cellular operator and is turned on through a downlink message on a cell-by-cell basis.
However, this may not just be a problem between LTE and narrowband public safety. Any mobile receivers operating in the 700 MHz spectrum may be affected by the OOBE because the 1 MHz guard band between the base and mobile transmit bands may be insufficient for significant attenuation of broadband signals. On the other hand, the 1 MHz guard band between Block C and the D/Public Safety Spectrum Trust (PSST) blocks may provide sufficient room for filters on the broadband base transmitters to attenuate the base-generated OOBE, reducing potential interference near base stations.
The operation of two unsynchronized TDD systems in adjacent carriers is another scenario where guard bands may be required. In TDD, UL and DL subframes operate on the same carrier. Without any guard band, cross UL and DL subframe interference may lead to severe performance degradation at the UE receiver (e.g., due to UE to UE interference) as well as at the BS receiver (e.g., due to BS to BS interference). This cross UL/DL subframe interference may even lead to complete disruption of the service, for example, if UEs on two carriers are quite close. Therefore, a guard band is required between the two unsynchronized TDD carriers.
The operation of a TDD system and an FDD system using adjacent carriers is another scenario where guard bands may be required. The adjacent TDD and FDD carriers may belong to different frequency bands, but the bands are adjacent. An example is operation in 2.6 GHz, for example, LTE FDD band 7 and LTE TDD band 38. The TDD band 38 operates in the center of FDD band 7. Therefore, to reduce, avoid, and/or minimize inter-system interference, restricted use of 5 MHz of spectrum on each edge of the TDD band 38 may be recommended. The restricted usage corresponds to the guard band in a sense that both LTE TDD UE and LTE TDD BS transmissions at the edges of band 38 are allowed at very low output power.
Multi-Carrier and Carrier Aggregation System
To increase/enhance peak-rates within a technology, multi-carrier or carrier aggregation solutions are known. Each carrier in a multi-carrier or carrier aggregation system may generally be termed as a component carrier (CC) or sometimes is also referred to as a cell. The term carrier aggregation (CA) may also be referred to using terms such as “multi-carrier system”, “multi-cell operation”, “multi-carrier operation”, “multi-carrier” transmission, and/or reception. This means the CA is used for transmission of signaling and data in the uplink and downlink directions. One of the CCs is the primary carrier or anchor carrier and the remaining CCs are called secondary or supplementary carriers. Generally, the primary or anchor CC carries the essential UE specific signaling. The primary CC exists in both uplink and direction CA. The network may assign different primary carriers to different UEs operating in the same sector or cell. Thanks to carrier aggregation, the UE has more than one serving cell: one primary serving cell and one or more secondary serving cell(s). The serving cell may alternatively be referred to as a primary cell (PCell) or primary serving cell (PSC). Similarly the secondary serving cell may be referred to as a secondary cell (SCell) or secondary serving cell (SSC). Regardless of the terminology, the PCell and SCell(s) enable the UE to receive and transmit data. More specifically the PCell and SCell exist in DL and UL for the reception and transmission of data by the UE. The remaining non-serving cells on the Primary Component Carrier (PCC) and Secondary Component Carrier (SCC) are called neighbor cells.
The CCs belonging to the CA may belong to the same frequency band (also referred to as intra-band CA) or to a different frequency band(s) (inter-band CA) or any combination thereof (e.g., 2 CCs in band A and 1 CC in band B). The carriers in intra-band CA can be adjacent (also referred to as contiguous) or non-adjacent (also referred to as non-contiguous). In non-adjacent intra-band CA, the carriers in gaps may typically be used by other operators. Typically, in intra-band CA, the UE may require a single RF receiver chain and RF transmitter chain to receive and transmit the aggregated carriers respectively, especially when the total aggregated carriers are within a certain limit (e.g. 20 MHz in total for High Speed Packet Access (HSPA) or 40 MHz in total for LTE). Otherwise, the UE may have to implement multiple RF transmitter/receiver chains for an aggregated larger number of carriers and particularly in case of non-contiguous CA.
The inter-band CA including carriers distributed over two bands is also referred to as dual-band-dual-carrier High Speed Downlink Packet Access (DB-DC-HSDPA) in HSPA. Furthermore the CCs in intra-band CA may be adjacent or non-adjacent in frequency domain (also referred to as intra-band non-adjacent CA). A hybrid CA including intra-band adjacent CA, intra-band non-adjacent CA, and inter-band CA is also possible.
In HSPA release 10 (also referred to as 4C-HSDPA), up to 4 DL carriers can be aggregated where the DL carriers or DL cells may belong to the same frequency band or may be split over two different frequency bands (e.g. 3 adjacent DL carriers in band I at 2.1 GHz and 1 DL carrier in band VIII at 900 MHz). In HSPA Rel-11 (also referred to as 8C-HSDPA), up to 8 DL carriers may be aggregated, and the DL carriers may be distributed over 2 or even more bands. In the present version of the HSPA and LTE specifications (i.e., rel-10), all the carriers that belong to one frequency band may have to be adjacent when configured by higher layers (e.g. RRC or Radio Resource Control). The operation on non-adjacent carriers within the same band, however, may result from the carrier activation/deactivation, which is performed by the lower layers (e.g., the MAC or Media Access Control layer). As stated above, however, the non-adjacent carriers within the same band may also be configurable provided that the UE supports this capability.
In principle, up to 5 DL carriers and 5 UL carriers (each of up to 20 MHz) may be aggregated by the UE in LTE intra-band CA. Even more carriers may be introduced in future releases. UE requirements exist for at least 2 DL carriers and 2 UL carriers (e.g., up to 40 MHz in UL and DL) according to release 10. The intra-band non-contiguous CA is also possible in LTE both in the DL and UL. The UE may use single RF chain or multiple RF chains depending upon the aggregated bandwidth.
In LTE inter-band CA, up to 5 DL and 5 UL carriers (each of up to 20 MHz and belonging to different bands) can be aggregated by the UE. Even additional carriers belonging to different bands may be introduced in future releases. UE requirements exist for at least 2 DL carriers belong to 2 different bands and 1 UL carriers in release 10. The requirements for 2 UL inter-band CA are being introduced in release 11. Typically, for inter-band CA, the UE has an independent RF chain for each CC which may belong to a different frequency band.
The CCs in CA may or may not be co-located in the same site or base station. For example, the CCs may originate (i.e., may be transmitted/received) at different locations (e.g. from non-located BS, RRH or remote radio head, or RRU or remote radio unit). Examples of combined CA and multi-point communication include DAS (Distributed Antenna System), RRH (Remote Radio Head), RRU (Remote Radio Unit), CoMP (coordinated multip-point), and multi-point transmission/reception, etc. Embodiments discussed herein may also apply to multi-point carrier aggregation systems.
Various of the above described approaches may exhibit one or more of the following deficiencies:
1) Static guard band allocation is not an efficient way of utilizing the spectrum.
2) Static guard bands may not solve all interference problems unless the guard band allocation is very wide resulting in low spectrum utilization.
3) The guard band is required only when 2 systems which require a guard band are in the same geographical area. However in a large network the two systems may not be operating in all the sites at the same time. However, the existing methods enable guard band in static manner without considering the real time situation. This leads to wastage of spectrum.
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in any application claiming priority from this application and are not admitted to be prior art by inclusion in this section.